In wireless communication systems, multi-level modulation is used to increase a channel capacity. For example, in quadrature phase shift keying (QPSK), 2 bits are mapped in one symbol. In quadrature amplitude modulation (16QAM), 4 bits are mapped in one symbol. In 64QAM, 6 bits are mapped in one symbol. In the 3rd Generation Partnership Project (3GPP), standard specifications of Long Term Evolution (LTE) for use in portable telephone systems are under discussion.
A receiver (receiving apparatus) includes a demodulator and a decoder. The demodulator performs, for example, a soft decision on a received symbol and outputs a result as soft decision value. The soft decision value represents a likelihood of a determination of each bit as being “0” or “1” for the received symbol. The soft decision value output from the demodulator is temporarily stored in a memory. The decoder calculates estimated bits from the soft decision value stored in the memory. Each estimated bit is an estimated value for a transmitted bit.
In the receiver configured in the above-described manner, the soft decision value may be converted from a fixed point format into a floating point format, and resultant data may be stored. Representing the soft decision value in the floating point format allows the decoder to reduce a calculation amount associated with the calculation of the estimated bit. Each floating-point number includes a sign, a mantissa, and an exponent.
A description of a related technique may be found, for example, in 3GPP TS 36.212 V8.8.0.